Originally Posted by zimmy
The part you are missing is that you have to kill either one small fish or one large fish, you also have to add in the recruitment from the fish that come from the eggs. You also have to look at the mortality rates. You w0uld have to establish the population denisty in each age/size group and then evaluate the mortality in each scenario, then calculate the reproductive potential. It is an algebriac problem, not arithmetic. By the way, if you want to use your math to get an idea, kill one small fish and do your calculations for three time periods. Then kill the 40" and do the calculations for three years. That will give you some idea. Then multiply by millions and look at the difference. It isn't really valid, but it at least gives you an idea what happens when you kill a fish.
I'll do a quick estimate of the two scenarios using the math the way you did it, but with one fish killed. By year 10the numbers are even less valid as 35-40% of breeding females are harvested each year.
Kill one small:
Year 1
2x28"= 1,403,000
1 x 40 =1,985,454
(big fish +500,000 increasing each year for 5 years)
year 5
2x28= 2,805,000
1x 50 = 3,818,181.82
(1 million per year positive, diminishing over next 5 years)
roughly 6.6 million eggs annually combined
year 10
2x37= 5427675
(I will let the big fish be dead. The eggs it produced for years 2-4 and 6-9 more than make up for the difference.)
Scenario 2: Kill the big fish, protect the little fish
year one
3x 28 = 2,125,000
big fish dead
year 5
3 x 37 = 4,250,000
(would probably be 2 x 37 accounting for mortality, so 2,805,000 is more realistic)
It takes 5 years from the time they are 28" for those 3 fish to get to the point where the total release by three 37" equals the release of one 50lber.
Scenario one results in millions of more eggs annually and a tremendously greater recruitment. In scenario two, without the 40" fish in the mix, millions of fewer eggs annually leads to an exponentially smaller population in the future. Now you can imagine a scenario where either a 40" or 28" is killed, but there are 3 small fish and 2 40" fish. One has to die. Those two 40" fish will produce tens of millions more eggs in the scenario where a 28" is harvested then if a 40" is harvested.
There is no comparison between the ability for big fish to aid in recruitment compared to small fish.
eggs per year combined
years scenario 1 (kill a 28") vs. scenario 2 (kill a 40")
1-4 : ~3.5 million vs. ~2,125,000
5-9 : ~ 6.6 million vs. ~4,250,0000
Over the 10 year period, the kill a 28" group produce roughly 50 million eggs, the kill a 40" ~32 million.
once the breeding potential of recruitment classes are included it is an astronomical difference
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